Primary Alkaline Battery With Integrated In-Cell Resistances

ABSTRACT

The invention is directed toward a primary AA alkaline battery. The primary AA alkaline battery includes an anode; a cathode; an electrolyte; and a separator between the anode and the cathode. The anode includes an electrochemically active anode material. The cathode includes an electrochemically active cathode material. The electrolyte includes potassium hydroxide. The primary AA alkaline battery has an integrated in-cell ionic resistance (R i ) at 22° C. of less than about 39 mΩ. The separator has a porosity of greater than 70%.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/968,725, filed May 1, 2018, which is a continuation of U.S. patentapplication Ser. No. 14/632,223, filed Feb. 26, 2015, which claims thebenefit under 35 U.S.C. § 119(e) of U.S. provisional patent applicationSer. No. 62/015,276, filed Jun. 20, 2014, the entire disclosures ofwhich are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a primary alkaline battery with integratedin-cell resistances and to a method for determining such in-cellintegrated resistances.

BACKGROUND OF THE INVENTION

Electrochemical cells, or batteries, are commonly used as electricalenergy sources. A battery contains a negative electrode, typicallycalled the anode, and a positive electrode, typically called thecathode. The anode contains an electrochemically active anode materialthat can be oxidized. The cathode contains an electrochemically activecathode material that can be reduced. The electrochemically active anodematerial is capable of reducing the electrochemically active cathodematerial. A separator is disposed between the anode and the cathode. Thebattery components are disposed in a can, or housing, that is typicallymade from metal.

When a battery is used as an electrical energy source in an electronicdevice, electrical contact is made to the anode and the cathode,allowing electrons to flow through the device and permitting therespective oxidation and reduction reactions to occur to provideelectrical power to the electronic device. An electrolyte is in contactwith the anode, the cathode, and the separator. The electrolyte containsions that flow through the separator between the anode and cathode tomaintain charge balance throughout the battery during discharge.

There is a growing need to make batteries that are better suited topower contemporary electronic devices such as toys; remote controls;audio devices; flashlights; digital cameras and peripheral photographyequipment; electronic games; toothbrushes; radios; and clocks. To meetthis need, batteries may include higher loading of electrochemicallyactive anode and/or cathode materials to provide increased capacity andservice life. Batteries, however, also come in common sizes, such as theAA, AAA, AAAA, C, and D battery sizes, that have fixed externaldimensions and constrained internal volumes. The ability to increaseelectrochemically active material loading alone to achieve betterperforming batteries is thus limited.

There exists a need to provide an alkaline battery with optimizedintegrated in-cell resistances to substantially increase overall batteryperformance, such as power capability and service life.

SUMMARY OF THE INVENTION

In one embodiment, the invention is directed toward a primary AAalkaline battery. The primary AA alkaline battery includes an anode; acathode; an electrolyte; and a separator between the anode and thecathode. The anode includes an electrochemically active anode material.The cathode includes an electrochemically active cathode material. Theelectrolyte includes potassium hydroxide. The primary AA alkalinebattery has an integrated in-cell ionic resistance (R_(i)) at 22° C. ofless than about 39 mΩ. The electrochemically active cathode materialincludes electrolytic manganese dioxide. The electrolytic manganesedioxide has a specific cathode loading from about 2.9 g/cm³ to about3.45 g/cm³. The separator has a porosity of greater than 75%.

In another embodiment, the invention is directed toward a method fordetermining the integrated in-cell resistance of a battery. The methodincludes the step of providing an electrolyte. The method also includesthe step of measuring a resistance of the electrolyte, R_(el-te(ti)), ata temperature t_(i). The method further includes the step of measuring aresistance of the electrolyte, R_(el-te(ti)), at a temperature t_(j).The method also includes the step of calculating a ratio of theresistance of the electrolyte, R_(el-te(ti)), at the temperature t_(i)to the resistance of the electrolyte, R_(el-te(ti)), at the temperaturet_(i) per Equation 6. The method further includes the step of providinga battery including the electrolyte. The method also includes the stepof measuring an ohmic resistance of the battery, R_(i), at thetemperature t_(i). The method includes the step of measuring an ohmicresistance of the battery, R_(i), at the temperature t_(j). In addition,the method includes the step of calculating an integrated in-cellelectronic resistance, R_(e), of the battery per Equation 7. The methodalso includes the step of calculating an integrated in-cell ionicresistance, R_(i(ti)), of the battery at the temperature t_(i) perEquation 8. The method includes the step of calculating an integratedin-cell ionic resistance, R_(i(ti)), of the battery at the temperaturet_(j) per Equation 8.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter, which is regarded as formingthe present invention, it is believed that the invention will be betterunderstood from the following description taken in conjunction with theaccompanying drawings.

FIG. 1 is a cross-section of a primary alkaline battery with integratedin-cell resistances of the present invention.

FIG. 2 is a process flow diagram of an embodiment of a method forcalculating integrated in-cell resistances of the present invention.

FIG. 3 is a perspective view of a primary alkaline battery withintegrated in-cell resistances of the present invention including avoltage indicator.

DETAILED DESCRIPTION OF THE INVENTION

Electrochemical cells, or batteries, may be primary or secondary.Primary batteries are meant to be discharged, e.g., to exhaustion, onlyonce and then discarded. Primary batteries are described, for example,in David Linden, Handbook of Batteries (4^(th) ed. 2011). Secondarybatteries are intended to be recharged. Secondary batteries may bedischarged and recharged many times, e.g., more than fifty times, ahundred times, or more. Secondary batteries are described, for example,in David Linden, Handbook of Batteries (4^(th) ed. 2011). Accordingly,batteries may include various electrochemical couples and electrolytecombinations. Although the description and examples provided herein aregenerally directed towards primary alkaline electrochemical cells, orbatteries, it should be appreciated that the invention applies to bothprimary and secondary batteries of aqueous, nonaqueous, ionic liquid,and solid state systems. Primary and secondary batteries of theaforementioned systems are thus within the scope of this application andthe invention is not limited to any particular embodiment.

Referring to FIG. 1, there is shown a primary alkaline electrochemicalcell, or battery, 10 including a cathode 12, an anode 14, a separator16, and a housing 18. Battery 10 also includes current collector 20,seal 22, and an end cap 24. The end cap 24 serves as the negativeterminal of the battery 10. A positive pip 26 is at the opposite end ofthe battery 10 from the end cap 24. The positive pip 26 may serve as thepositive terminal of the battery 10. An electrolytic solution isdispersed throughout the battery 10. The cathode 12, anode 14, separator16, electrolyte, current collector 20, and seal 22 are contained withinthe housing 18. Battery 10 can be, for example, a AA, AAA, AAAA, C, or Dalkaline battery.

The housing 18 can be of any conventional type of housing commonly usedin primary alkaline batteries and can be made of any suitable basematerial, for example cold-rolled steel or nickel-plated cold-rolledsteel. The housing 18 may have a cylindrical shape. The housing 18 maybe of any other suitable, non-cylindrical shape. The housing 18, forexample, may have a shape comprising at least two parallel plates, suchas a rectangular, square, or prismatic shape. The housing 18 may be, forexample, deep-drawn from a sheet of the base material, such ascold-rolled steel or nickel-plated steel. The housing 18 may be, forexample, drawn into a cylindrical shape. The housing 18 may have atleast one open end. The housing 18 may have a closed end and an open endwith a sidewall therebetween. The interior surface of the sidewall ofthe housing 18 may be treated with a material that provides a lowelectrical-contact resistance between the interior surface of thesidewall of the housing 18 and an electrode, such as the cathode 12. Theinterior surface of the sidewall of the housing 18 may be plated, e.g.,with nickel, cobalt, and/or painted with a carbon-loaded paint todecrease contact resistance between, for example, the internal surfaceof the sidewall of the housing 18 and the cathode 12.

The current collector 20 may be made into any suitable shape for theparticular battery design by any known methods within the art. Thecurrent collector 20 may have, for example, a nail-like shape. Thecurrent collector 20 may have a columnar body and a head located at oneend of the columnar body. The current collector 20 may be made of metal,e.g., zinc, copper, brass, silver, or any other suitable material. Thecurrent collector 20 may be optionally plated with tin, zinc, bismuth,indium, or another suitable material presenting a low electrical-contactresistance between the current collector 20 and, for example, the anode14. The plating material may also exhibit an ability to suppress gasformation when the current collector 20 is contacted by the anode 14.

The seal 22 may be prepared by injection molding a polymer, such aspolyamide, polypropylene, polyetherurethane, or the like; a polymercomposite; and mixtures thereof into a shape with predetermineddimensions. The seal 22 may be made from, for example, Nylon 6,6; Nylon6,10; Nylon 6,12; Nylon 11; polypropylene; polyetherurethane;co-polymers; composites; and mixtures thereof. Exemplary injectionmolding methods include both the cold runner method and the hot runnermethod. The seal 22 may contain other known functional materials such asa plasticizer, a crystalline nucleating agent, an antioxidant, a moldrelease agent, a lubricant, and an antistatic agent. The seal 22 mayalso be coated with a sealant. The seal 22 may be moisturized prior touse within the battery 10. The seal 22, for example, may have a moisturecontent of from about 1.0 weight percent to about 9.0 weight percentdepending upon the seal material. The current collector 20 may beinserted into and through the seal 22.

The end cap 24 may be formed in any shape sufficient to close therespective battery. The end cap 24 may have, for example, a cylindricalor prismatic shape. The end cap 24 may be formed by pressing a materialinto the desired shape with suitable dimensions. The end cap 24 may bemade from any suitable material that will conduct electrons during thedischarge of the battery 10. The end cap 24 may be made from, forexample, nickel-plated steel or tin-plated steel. The end cap 24 may beelectrically connected to the current collector 20. The end cap 24 may,for example, make electrical connection to the current collector 20 bybeing welded to the current collector 20. The end cap 24 may alsoinclude one or more apertures, such as holes, for venting any gaspressure that may build up under the end cap 24 during a gassing eventwithin the battery 10, for example, during deep discharge or reversal ofthe battery 10 within a device, that may lead to rupturing of the vent.

Cathode 12 includes one or more electrochemically active cathodematerials. The electrochemically active cathode material may includemanganese oxide, manganese dioxide, electrolytic manganese dioxide(EMD), chemical manganese dioxide (CMD), high power electrolyticmanganese dioxide (HP EMD), lambda manganese dioxide, gamma manganesedioxide, beta manganese dioxide, and mixtures thereof. Otherelectrochemically active cathode materials include, but are not limitedto, silver oxide; nickel oxide; nickel oxyhydroxide; copper oxide;copper salts, such as copper iodate; bismuth oxide; high-valence nickelcompound; high-valence iron compound; oxygen; and mixtures thereof. Thenickel oxide can include nickel hydroxide, nickel oxyhydroxide, cobaltoxyhydroxide-coated nickel oxyhydroxide, delithiated layered lithiumnickel oxide, partially delithiated layered nickel oxide, and mixturesthereof. The nickel hydroxide or oxyhydroxide can include beta-nickeloxyhydroxide, gamma-nickel oxyhydroxide, and/or intergrowths ofbeta-nickel oxyhydroxide and/or gamma-nickel oxyhydroxide. The cobaltoxyhydroxide-coated nickel oxyhydroxide can include cobaltoxyhydroxide-coated beta-nickel oxyhydroxide, cobalt oxyhydroxide-coatedgamma-nickel oxyhydroxide, and/or cobalt oxyhydroxide-coatedintergrowths of beta-nickel oxyhydroxide and gamma-nickel oxyhydroxide.The high-valence nickel compound may, for example, include tetravalentnickel. The high-valence iron compound may, for example, includehexavalent iron.

Cathode 12 may include a conductive additive, such as carbon particles,and a binder. The carbon particles are included in the cathode to allowthe electrons to flow through the cathode. The carbon particles may begraphite, such as expanded graphite and natural graphite; graphene,single-walled nanotubes, multi-walled nanotubes, carbon fibers; carbonnanofibers; and mixtures thereof. It is preferred that the amount ofcarbon particles in the cathode is relatively low, e.g., less than about10%, less than about 7.0%, less than about 4.25%, less than about 3.75%,less than about 3.5%, or even less than about 3.25%, for example fromabout 2.0% to about 3.25%. The lower carbon level enables inclusion of ahigher loading of electrochemically active material within the cathode12 without increasing the volume of the cathode 12 or reducing the voidvolume of the finished battery 10 (which must be maintained at or abovea certain level to prevent internal pressure from rising too high as gasis generated within the cell). Suitable expanded graphite may be, forexample, BNB-90 graphite available from TIMCAL Carbon & Graphite (Bodio,Switzerland).

Examples of binders that may be used in the cathode 12 includepolyethylene, polyacrylic acid, or a fluorocarbon resin, such as PVDF orPTFE. An example of a polyethylene binder is sold under the trade nameCOATHYLENE HA-1681 (available from Hoechst or DuPont). Examples of othercathode additives are described in, for example, U.S. Pat. Nos.5,698,315, 5,919,598, 5,997,775 and 7,351,499.

The amount of electrochemically active cathode material within thecathode 12 may be referred to as the cathode loading. The loading of thecathode 12 may vary depending upon the electrochemically active cathodematerial used within, and the cell size of, the battery 10. For example,AA batteries with an EMD electrochemically active cathode material mayhave a cathode loading of at least about 9.0 grams of EMD. The cathodeloading may be, for example, at least about 9.5 grams of EMD. Thecathode loading may be, for example, from about 9.7 grams to about 11.5grams of EMD. The cathode loading may be from about 9.7 grams to about11.0 grams of EMD. The cathode loading may be from about 9.8 grams toabout 11.2 grams of EMD. The cathode loading may be from about 9.9 gramsto about 11.5 grams of EMD. The cathode loading may be from about 10.4grams to about 11.5 grams of EMD. For a AAA battery, the cathode loadingmay be from about 4.0 grams to about 6.0 grams of EMD. For a AAAAbattery, the cathode loading may be from about 2.0 grams to about 3.0grams of EMD. For a C battery, the cathode loading may be from about25.0 grams to about 29.0 grams of EMD. For a D battery, the cathodeloading may be from about 54.0 grams to about 70.0 grams of EMD.

The cathode components, such as electrochemically active cathodematerial(s), carbon particles, and binder, may be combined with aliquid, such as an aqueous potassium hydroxide electrolyte; blended; andpressed into pellets for use in the manufacture of a finished battery.For optimal cathode pellet processing, it is generally preferred thatthe cathode material have a moisture level in the range of about 2.5% toabout 5%, more preferably about 2.8% to about 4.6%. The pellets, afterbeing placed within a housing during the battery manufacturing process,are typically re-compacted to form a uniform cathode.

It is generally preferred that the cathode 12 be substantially free ofnonexpanded graphite. Nonexpanded graphite particles may providelubricity to the cathode pellet forming equipment. Nonexpanded graphite,however, is significantly less conductive than expanded graphite and itmay be necessary to use more nonexpanded graphite in order to obtain thesame cathode conductivity of a cathode containing expanded graphite.While not preferred, the cathode may include low levels of unexpandedgraphite, however this will compromise the reduction in graphiteconcentration that can be obtained while maintaining a particularcathode conductivity.

The cathode 12 will have a porosity that may be calculated at the timeof cathode manufacture. The porosity of the cathode may be calculated atthe time of manufacturing, for example after the cathode pelletprocessing, since the porosity of the cathode 12 within a battery 10will change over time due to, inter alia, cathode swelling associatedwith electrolyte wetting of the cathode and battery discharge. Theporosity of the cathode may be calculated as follows. The true densityof each solid cathode component may be taken from a reference book, forexample Lange's Handbook of Chemistry (16^(th) ed. 2005). The solidsweight of each of the cathode components are defined by the batterydesign. The solids weight of each cathode component may be divided bythe true density of each cathode component to determine the cathodesolids volume. The volume occupied by the cathode within the battery isdefined, again, by the battery design. The volume occupied by thecathode may be calculated by a computer-aided design (CAD) program. Theporosity may be determined by the following formula:

Cathode Porosity=[1−(cathode solids volume÷cathode volume)]×100

For example, the cathode 12 of a AA battery may include about 10.90grams of manganese dioxide and about 0.401 grams of graphite (BNB-90) assolids within the cathode 12. The true densities of the manganesedioxide and graphite may be, respectively, about 4.45 g/cm³ and about2.15 g/cm³. Dividing the weight of the solids by the respective truedensities yields a volume occupied by the manganese dioxide of about2.45 cm³ and by the graphite of about 0.19 cm³. The total solids volumeis about 2.64 cm³. The designer may select the volume occupied by thecathode 12 to be about 3.473 cm³. Calculating the cathode porosity perthe equation above [1-(2.64 cm³÷ 3.473 cm³)] yields a cathode porosityof about 0.24, or 24%. The cathode porosity may be from about 15% toabout 45% and is preferably between about 22% and about 35%.

The amount of electrochemically active cathode material within a givenvolume of the cathode 12 may be referred to as the specific cathodeloading. The volume occupied by the cathode 12 within the battery 10, asis discussed above, may be defined by the battery design. The volumeoccupied by the cathode 12 may be calculated by a computer-aided design(CAD) program. The specific cathode loading may be, for example, greaterthan about 2.9 grams of EMD per cubic centimeter of cathode volume. Thespecific cathode loading may be, for example, from about 2.9 grams ofEMD per cubic centimeter of cathode volume to about 3.45 grams of EMDper cubic centimeter of cathode volume. The specific cathode loading maybe, for example, from about 3.0 grams of EMD per cubic centimeter ofcathode volume to about 3.36 grams of EMD per cubic centimeter ofcathode volume. The specific cathode loading may be, for example, fromabout 3.10 grams of EMD per cubic centimeter of cathode volume to about3.25 grams of EMD per cubic centimeter of cathode volume.

The electrochemically active cathode material may consist of particles.The particles of electrochemically active cathode material may have asurface area. The surface area of the particles of electrochemicallyactive cathode material may be determined by any method known in theart. For example, the surface area of the particles of electrochemicallyactive cathode material may be determined using the Brauner-Emmet-Teller(BET) technique. The BET surface area of the particles ofelectrochemically active cathode material may be, for example, greaterthan 15 m²/g. The BET surface area of the particles of electrochemicallyactive cathode material may be, for example, from about 15 m²/g to about35 m²/g. The BET surface area of the particles of electrochemicallyactive cathode material may be, for example, from about 18 m²/g to about28 m²/g. The BET surface area of the particles of electrochemicallyactive cathode material may be, for example, from about 20 m²/g to about25 m²/g.

Anode 14 can be formed of at least one electrochemically active anodematerial, a gelling agent, and minor amounts of additives, such asgassing inhibitor. The electrochemically active anode material mayinclude zinc; cadmium; iron; metal hydride, such as AB₅, AB₂, and A₂B₇;alloys thereof; and mixtures thereof.

The amount of electrochemically active anode material within the anode14 may be referred to as the anode loading. The loading of the anode 14may vary depending upon the electrochemically active anode material usedwithin, and the cell size of, the battery 10. For example, AA batterieswith a zinc electrochemically active anode material may have an anodeloading of at least about 3.3 grams of zinc. The anode loading may be,for example, at least about 4.0, about 4.3, about 4.6 grams, about 5.0grams, or about 5.5 grams of zinc. AAA batteries, for example, with azinc electrochemically active anode material may have an anode loadingof at least about 1.9 grams of zinc. For example, the anode loading mayhave at least about 2.0 or about 2.1 grams of zinc. AAAA batteries, forexample, with a zinc electrochemically active anode material may have ananode loading of at least about 0.6 grams of zinc. For example, theanode loading may have at least about 0.7 to about 1.0 grams of zinc. Cbatteries, for example, with a zinc electrochemically active anodematerial may have an anode loading of at least about 9.5 grams of zinc.For example, the anode loading may have at least about 10.0 to about15.0 grams of zinc. D batteries, for example, with a zincelectrochemically active anode material may have an anode loading of atleast about 19.5 grams of zinc. For example, the anode loading may haveat least about 20.0 to about 30.0 grams of zinc.

The electrochemically active anode material may consist of particles.The particles of electrochemically active anode material may have asurface area. The surface area of the particles of electrochemicallyactive anode material may be determined by any method known in the art.For example, the surface area of the particles of electrochemicallyactive anode material may be determined using the Brauner-Emmet-Teller(BET) technique. The BET surface area of the particles ofelectrochemically active anode material may be, for example, greaterthan 0.040 m²/g. The BET surface area of the particles ofelectrochemically active anode material may be, for example, from about0.0410 m²/g to about 0.0600 m²/g. The BET surface area of the particlesof electrochemically active anode material may be, for example, fromabout 0.0450 m²/g to about 0.0550 m²/g. The BET surface area of theparticles of electrochemically active anode material may be, forexample, from about 0.0490 m²/g to about 0.0510 m²/g.

The particles of the electrochemically active anode material may have aparticle size. The electrochemically active anode material may comprisea Gaussian distribution of particle sizes. For example, the averageparticle size of electrochemically active anode material may be greaterthan about 10 μm and less than about 300 μm. The average particle sizeof electrochemically active anode material may be greater than about 50μm and less than about 300 μm. The average particle size ofelectrochemically active anode material may be greater than about 60 μmand less than about 250 μm. The average particle size ofelectrochemically active anode material may be greater than about 75 μmand less than about 150 μm. The average particle size ofelectrochemically active anode material may be greater than about 10 μmand less than about 70 μm. The average particle size ofelectrochemically active anode material may be greater than about 20 μmand less than about 60 μm. The average particle size ofelectrochemically active anode material may be greater than about 30 μmand less than about 50 μm. The electrochemically active anode materialmay comprise a multi-modal distribution of particle sizes, for example abi-modal or tri-modal distribution of particle sizes. A multi-modaldistribution refers to a distribution having at least two distinctpeaks. Thus, a plot of relative percent of particles as a function ofparticle size for electrochemically active anode material having amulti-modal distribution of particle sizes would have at least twodistinct peaks. One mode of a particle size distribution may compriseabout 10% to about 90% of a sample with average particle size in thismode ranging from about 10 μm to about 70 μm. A second mode of aparticle size distribution may comprise about 10% to about 90% of thesame sample with an average particle size in this mode ranging fromabout 50 μm to about 300 μm. An example of multi-modal particle sizedistribution for zinc as the electrochemically active anode material maybe a bi-modal distribution where from about 10% to about 35% of themixture may have an average particle size of between about 10 μm andabout 70 μm and the remaining about 65% to about 90% of the mixture mayhave an average particle size distribution of between about 50 μm andabout 300 μm.

Examples of a gelling agent that may be used include a polyacrylic acid;a grafted starch material; a salt of a polyacrylic acid; acarboxymethylcellulose; a salt of a carboxymethylcellulose (e.g., sodiumcarboxymethylcellulose); or combinations thereof. The anode may includea gassing inhibitor that may include an inorganic material, such asbismuth, tin, or indium. Alternatively, the gassing inhibitor caninclude an organic compound, such as a phosphate ester, an ionicsurfactant or a nonionic surfactant.

The electrolyte may be dispersed throughout the cathode 12, the anode 14and the separator 16. The electrolyte comprises an ionically conductivecomponent in an aqueous solution. The ionically conductive component maybe a hydroxide. The hydroxide may be, for example, sodium hydroxide,potassium hydroxide, lithium hydroxide, cesium hydroxide, and mixturesthereof. The ionically conductive component may also include a salt. Thesalt may be, for example, zinc chloride, ammonium chloride, magnesiumperchlorate, magnesium bromide, and mixtures thereof. The concentrationof the ionically conductive component may be selected depending on thebattery design and its desired performance. An aqueous alkalineelectrolyte may include a hydroxide, as the ionically conductivecomponent, in a solution with water. The concentration of the hydroxidewithin the electrolyte may be from about 0.25 to about 0.40, or fromabout 25% to about 40%, on a weight basis of the total electrolytewithin the battery 10. For example, the hydroxide concentration of theelectrolyte may be from about 0.25 to about 0.32, or from about 25% toabout 32%, on a weight basis of the total electrolyte within the battery10. The aqueous alkaline electrolyte may also include zinc oxide (ZnO)dissolved within it. The ZnO may serve to suppress zinc corrosion withinthe anode. The concentration of ZnO included within the electrolyte maybe less than about 3% by weight of the total electrolyte within thebattery 10. The ZnO concentration, for example, may be from about 1% byweight to about 3% by weight of the total electrolyte within the battery10.

The total weight of the aqueous alkaline electrolyte within a AAalkaline battery, for example, may be from about 3.0 grams to about 4.0grams. The total weight of the electrolyte within a AA batterypreferably may be, for example, from about 3.3 grams to about 3.8 grams.The total weight of the electrolyte within a AA battery may be, forexample, from about 3.4 grams to about 3.65 grams. The total weight ofthe aqueous alkaline electrolyte within a AAA alkaline battery, forexample, may be from about 1.0 grams to about 2.0 grams. The totalweight of the electrolyte within a AAA battery may be, for example, fromabout 1.2 grams to about 1.8 grams. The total weight of the electrolytewithin a AAA battery may be, for example, from about 1.4 grams to about1.6 grams.

Separator 16 comprises a material that is wettable or wetted by theelectrolyte. A material is said to be wetted by a liquid when thecontact angle between the liquid and the surface is less than 90° orwhen the liquid tends to spread spontaneously across the surface; bothconditions normally coexist. Separator 16 may comprise woven or nonwovenpaper or fabric. Separator 16 may include a layer of, for example,cellophane combined with a layer of non-woven material. The separatoralso can include an additional layer of non-woven material. Theseparator material may be thin. The separator, for example, may have adry thickness of less than 150 micrometers (microns). The separator, forexample, may have a dry thickness of less than 100 microns. Theseparator preferably has a dry thickness from about 70 microns to about90 microns, more preferably from about 70 microns to about 75 microns.The separator, for example, may have a wet thickness of less than 185micrometers (microns). The separator, for example, may have a wetthickness from about 90 microns to about 180 microns. The separator, forexample, may have a wet thickness from about 100 microns to about 170microns. The separator, for example, may have a wet thickness from about110 microns to about 130 microns. The separator has a basis weight of 40g/m² or less. The separator preferably has a basis weight from about, 15g/m² to about 40 g/m², and more preferably from about 20 g/m² to about30 g/m². The separator, for example, may have a density of greater than1.30 g/cm³. The separator may have a density from about 1.32 g/cm³ toabout 1.40 g/cm³. The separator may have a density from about 1.34 g/cm³to about 1.38 g/cm³. The separator, for example, may have a porosity ofgreater than about 70%. The separator may have a porosity from about 71%to about 85%. The separator may have a porosity from about 73% to about80%. The separator may have a porosity from about 75% to about 79%.

Separator 16 may have an air permeability value. The air permeabilityvalue of a separator may be characterized by the Sodim air permeabilitytester, as defined in ISO 2965. The Sodim air permeability tester isdesigned to measure the air permeability of papers and non-wovenmaterials. The tester measures the volume of gas that passes, at apressure of 1 kPa, through a predetermined cross-section of the materialduring one minute. The air permeability value of Separator 16 may befrom about 2000 cm³/cm²·min @ 1 kPa to about about 5000 cm³/cm²·min @ 1kPa. The air permeability value of Separator 16 may be from about 3000cm³/cm²·min @ 1 kPa to about 4000 cm³/cm²·min @ 1 kPa. The airpermeability value of Separator 16 may be from about 3500 cm³/cm²·min @1 kPa to about about 3800 cm³/cm²·min @ 1 kPa.

Area-specific resistance is a measured property of the combinedseparator and electrolyte that is influenced by separator properties,such as composition, thickness, air permeability, basis weight, andwettability, along with electrolyte properties, such as hydroxide andzincate concentration. The area-specific resistance of a combination ofa separator in an alkaline electrolyte may be from about 100 mOhm-cm² toabout 800 mOhm-cm². The area-specific resistance may be from about 200mOhm-cm² to about 500 mOhm-cm².

Battery discharge performance generally depends on a number of factors.One important factor is the ohmic resistance of the battery which, alongwith other factors, may affect discharge rate capability and dischargeefficiency of the battery. The ohmic resistance of a battery, R, is acombination of an integrated in-cell ionic resistance, R_(i), and anintegrated in-cell electronic resistance, R_(e), within the battery. Theintegrated in-cell ionic resistance, R_(i), may include the ionicresistance of the electrolyte in the pores of the separator, R_(is), aswell as the resistance of the electrolyte in the pores of the cathodeand the anode that are in proximity of the separator, R_(ip). Theresistance of the electrolyte in the pores of the electrode materials ofthe cathode and the anode that are located inside the porous matrix ofthe cathode and the anode may affect the integrated in-cell ionicresistance, R_(i). The integrated in-cell ionic resistance, R_(i), mayrepresent the effective ionic resistance of the electrolyte in the poresof the separator and the pores of the porous matrix of the cathode andthe anode. The resistance of the electrolyte in the pores of the cathodeand the anode, R_(ip), will depend on the porosity of the cathode andanode, wettability of the pores, pore distribution, particle size,morphology, wetted surface area, and conductivity of the electrolyte.The integrated in-cell ionic resistance, R_(i); the integrated in-cellelectronic resistance, R_(e); and the ohmic resistance, R, will impactthe battery discharge performance, particularly under high-drainconditions. The discharge performance of a battery may be improved by,for example, minimizing the integrated in-cell ionic resistance, R_(i);the integrated in-cell electronic resistance, R_(e); and the ohmicresistance, R, of a battery.

The actual thickness of the separator within an assembled battery isunknown since, for example, the static pressure between the anode andthe cathode may exert force on either side of the separator resulting ina compressed thickness. In addition, the static pressure between theanode and the cathode will vary during battery discharge as the densityof the cathode active material and the anode active material will changewith battery discharge. Also, the particle size and particle sizedistribution of the cathode components and the anode components mayaffect the thickness of the separator within an assembled battery. Inaddition, the particles of the cathode components and the anodecomponents may become embedded within the separator under suchconditions. The wettability and compressibility of the separator willalso affect the thickness of the separator within the assembled battery.To account for such conditions, an effective separator thickness,T_(cell), that reflects the difference in the integrated in-cell ionicresistance, R_(i), and the resistance of electrolyte in the pores of theseparator, R_(is). The effective separator thickness, T_(cell), may alsoreflect how effectively the anode is dispensed within the battery andhow much void space is created within the anode during the anodedispensing process. The effective separator thickness will also comprisethe resistance of the electrolyte in the pores of the cathode and theanode, R_(ip). The effective separator thickness, T_(cell)) will impactthe battery discharge performance, particularly under high-drainconditions. The discharge performance of a battery may be improved by,for example, minimizing the effective separator thickness, T_(cell).

The integrated in-cell ionic resistance, R_(i), may vary depending uponthe components within, and the size of, the battery 10. The integratedin-cell ionic resistance, R_(i), may also vary with temperature. Forexample, primary alkaline AA batteries may have an integrated in-cellionic resistance, R_(i), at 22° C. of less than about 39 mΩ. Theintegrated in-cell ionic resistance, R_(i), at 22° C. may be from about15 mΩ to about 39 mΩ. The integrated in-cell ionic resistance, R_(i), at22° C. may be from about 20 mΩ to about 36.5 mΩ.

The integrated in-cell electronic resistance, R_(e), may vary dependingupon the components within, and the size of, the battery 10. Theintegrated in-cell electronic resistance, R_(e), may also vary withtemperature. For example, primary alkaline AA batteries may have anintegrated in-cell electronic resistance, R_(e), at 22° C. of less thanabout 22 mΩ. The integrated in-cell electronic resistance, R_(e), at 22°C. may be from about 10 mΩ to about 19 mΩ.

The ohmic resistance, R, may vary depending upon the components within,and the size of, the battery 10. The ohmic resistance, R, may also varywith temperature. For example, primary alkaline AA batteries may have aohmic resistance, R, at 22° C. of less than about 57 mΩ. The ohmicresistance, R, at 22° C. may be from about 25 mΩ to about 56 mΩ.

The ionic resistance of the electrolyte in the pores of the separator,R_(is), can be estimated by measuring the area-specific resistance of aseparator impregnated by a certain electrolyte that will be used withina battery and adjusting the area-specific resistance to an interfacialarea of the separator within the battery. A method, however, ofmeasuring the resistance of the electrolyte in the pores of the cathodeand the anode, R_(is), is not known to exist. Similarly, a method ofdetermining the effective separator thickness, T_(cell), is also notknown to exist.

The integrated in-cell electronic resistance of the battery, R_(e), mayinclude the electronic resistance of the combined current path throughwhich electrons may flow during discharge of the battery. The currentpath may include all metal-metal contacts, both internal and external tothe battery; the housing; any metal substrates; any leads in electricalcontact with the housing; particle-to-particle contact of, for example,the graphite or zinc; and the like.

In some instances, the electronic resistance of various batterycomponents may be estimated. For example, the electronic resistance ofthe current collector may be measured. The electronic resistance ofother battery components is not easily determined. For example,measuring the electronic resistance of the cathode and the anode isdifficult and imprecise. The electronic resistance of the cathode andthe anode may be completed using a two or four electrode probemeasurement of voltage drop across the cathode and the anode. Thistechnique, however, includes high variability in measurement that mayinclude, for example, between about 20% to about 30% error in themeasurement. Thus, this technique may only be used only for estimatingthe electronic resistance of battery components to which the techniqueapplies.

The ohmic resistance of the battery, R, may be measured by applying adirect current (DC) pulse of short duration to the battery and measuringthe drop in battery voltage that corresponds to the application of theDC current. The internal resistance of the battery, R, may be determinedby calculating the voltage of the battery that corresponds to theapplied current according to Ohm's law. The overall value of theinternal resistance of the battery, R, may also be measured utilizingwhat is commonly referred to as electrochemical impedance. Bothtechniques, however, may only determine the overall impedance of thebattery, R, and may not discern specific resistances that are associatedwith the various battery components.

There exists a need to independently measure the integrated in-cellionic resistance, R_(i), and the integrated in-cell electronicresistance, R_(e), of a battery. There also exists a need to extract theresistance of the electrolyte in the pores of the cathode and the anode,R_(ip). In addition, there exists a need to estimate the effectivethickness of a separator within an assembled battery, T_(cell). Theindependent characterization of these parameters within a battery mayresult in optimized battery designs and increased battery dischargeperformance.

As is discussed above, the ohmic resistance of a battery, R, includes anintegrated in-cell ionic resistance component, R_(i), and an integratedin-cell electronic resistance component, R_(e). The integrated in-cellionic resistance, R_(i), and the integrated in-cell electronicresistance, R_(e), of a battery may be affected by temperature. Theworking range of a battery may be from about 0° C. to about 45° C. Theintegrated in-cell ionic resistance, R_(i), of a battery within thisworking range may be greatly affected by changes in temperature. Theintegrated in-cell electronic resistance, R_(e), of a battery withinthis working range of a battery is not, however, greatly affected bychanges in temperature.

The temperature dependence of the integrated in-cell ionic resistancemay be utilized to evaluate the integrated in-cell ionic resistance,R_(i), within a battery. It may be assumed that the integrated in-cellelectronic resistance, R_(e), of a battery within a given temperaturerange remains constant according to Equation 1 below:

R _(e(tt)) =R _(e(tj)) =R _(e)  (1)

where R_(e(ti)) is the integrated in-cell electronic resistance, in Ohms(Ω), of the battery at a temperature, t_(i), in degrees Celsius (° C.);R_(e(ti)) is the integrated in-cell electronic resistance, in Ohms (Ω),of the battery at a different temperature, in degrees Celsius (° C.);and R_(e) is the constant integrated in-cell electronic resistance, inOhms (Ω), of the battery at any temperature ranging from t_(i) to t_(j).

It may also be assumed that ratio of the integrated in-cell ionicresistances of the battery at different temperatures is equal to theratio of the two electrolyte resistances of the battery at the twodifferent temperatures according to Equation 2 below:

$\begin{matrix}{\frac{R_{{el} - {{te}{({ti})}}}}{R_{{el} - {{te}{({tj})}}}} = \frac{R_{i{({ti})}}}{R_{i{({tj})}}}} & (2)\end{matrix}$

where R_(el-te(ti)) is the resistivity of the electrolyte within thebattery, in Ohms (Ω), at a temperature, t_(i), in degrees Celsius (°C.); R_(el-te(tj)) is the resistivity of the electrolyte within thebattery, in Ohms (Ω), at a different temperature, t_(j), in degreesCelsius (° C.); R_(i(ti)) is the integrated in-cell ionic resistance ofthe battery, in Ohms (Ω), at a temperature, t_(i), in degrees Celsius (°C.); and R_(i(ti)) is the integrated in-cell ionic resistance of thebattery, in Ohms (Ω), at a different temperature, in degrees Celsius (°C.).

The ohmic resistance of the battery, R, at temperatures t_(i) and t_(j),respectively, may be expressed according to Equation 3 and Equation 4below:

R _(ti) =R _(e(ti)) +R _(i(ti))  (3)

R _(tj) =R _(e(tj)) +R _(i(tj))  (4)

where R_(ti) is the ohmic resistance within the battery, in Ohms (Ω), ata temperature, t_(i), in degrees Celsius (° C.) and R_(tj) is the ohmicresistance within the battery, in Ohms (Ω), at a different temperature,t_(j), in degrees Celsius (° C.).

Equation 2, utilizing Equations 1, 3, and 4, may be rewritten asEquation 5 below:

$\begin{matrix}{\frac{R_{{el} - {{te}{({ti})}}}}{R_{{el} - {{te}{({tj})}}}} = \frac{R_{ti} - R_{e}}{R_{tj} - R_{e}}} & (5)\end{matrix}$

The ratio of the resistivity of the electrolyte within the battery attemperature t_(i) to the resistivity of the electrolyte within thebattery at temperature t_(j) may be defined as X and may be written asEquation 6 below:

$\begin{matrix}{X = \frac{R_{{el} - {{te}{({ti})}}}}{R_{{el} - {{te}{({tj})}}}}} & (6)\end{matrix}$

Equation 5, utilizing Equation 6, may be rewritten as Equation 7 below:

$\begin{matrix}{R_{e} = \frac{R_{ti} - {X \cdot R_{tj}}}{1 - X}} & (7)\end{matrix}$

The ohmic impedance of a battery may be measured at specifictemperatures within a given temperature range using, for example, aSolartron Impedance Analyzer. In addition, the resistivity of theelectrolyte at a given temperature may be experimentally determinedusing, for example, a conductivity cell. The integrated in-cellelectronic resistances of the battery at the specific temperatures maybe determined using Equation (7) above along with the experimentallydetermined ohmic impedances and resistivity of the battery at thespecific temperatures. The integrated in-cell ionic resistance of thebattery at a specific temperature within the given temperature range maybe written as Equation (8) below:

R _(i(tt)) =R _(tt) −R _(e)  (8)

The capacitance of a battery, C_(p), at a given temperature may also beincluded within the above analysis. The capacitance of the battery,C_(p), at a given temperature may be measured utilizing, for example, aSolartron impedance analyzer. The capacitance of the battery at a giventemperature may be extracted from the Nyquist plots that result fromsuch analysis. The capacitance of the battery, C_(p), at a giventemperature will be proportional to the electrochemically active surfacearea of the cathode and the anode. The capacitance of the battery,C_(p), at a given temperature may be treated as a compliment to theresistance of the electrolyte in the pores of the cathode and the anodethat are in proximity of the separator.

The integrated in-cell ionic resistance, R_(i), of the battery that iscalculated using Equation 8 may be compared within the area-specificresistance of the separator/electrolyte combination that is normalizedto the anode-to-cathode interfacial area of the battery. The differencebetween the integrated in-cell ionic resistance, R_(i), of the batteryand the normalized area-specific resistance of the separator/electrolytecombination may provide information for characterizing the resistance ofthe electrolyte in the pores of the cathode and the anode that are inproximity of the separator, R_(ip), or to determine the effectivethickness of the separator within the battery, T_(cell). The batterydesigner may optimize the battery design and the assembly batteryassembly process to subsequently improve battery discharge performance,or determine the efficiency of the anode dispensing process, bymeasuring and adjusting, either alone or in combination, the integratedin-cell electronic resistance, R_(e); the integrated in-cell ionicresistance, R_(i); the integrated in-cell ionic resistance of theelectrolyte in the pores of the separator, R_(is), or area-specificresistance; the resistance of the electrolyte in the pores of thecathode and the anode that are in proximity of the separator, R_(ip);the effective thickness of the separator of a battery design, T_(cell);and the capacitance of the battery.

The above techniques for evaluating and optimizing the design of abattery may be completed at various states of battery discharge orcharge. The above techniques also apply to evaluating and optimizing thedesign of a battery at various states of storage. Determining thevarious parameters described above at various states of batterydischarge, battery charge, and battery storage may also help optimizebattery discharge performance and battery reliability.

Referring to FIG. 2, a method for determining the integrated in-cellresistances for a battery (200) is shown. The method includes providingan electrolyte (205). The method also includes the step of measuring aresistance of the electrolyte, R_(el-te(ti)), at a temperature t_(i)(210). The method also includes the step of measuring a resistance ofthe electrolyte, R_(el-te(tj)), at a temperature t_(j) (215). The methodalso includes the step of calculating the ratio of the resistance of theelectrolyte, R_(el-te(ti)), at a temperature t_(i) to the resistance ofthe electrolyte, R_(el-te(tj)), at a temperature t_(j) per Equation 6(220). The method also includes the step of providing a batteryincluding the electrolyte (225). The method also includes the step ofmeasuring the ohmic resistance of the battery, R_(i), at the temperaturet_(i) (230). The method also includes the step of measuring the ohmicresistance of the battery, R_(j), at the temperature t_(j) (235). Themethod also includes the step of calculating the integrated in-cellelectronic resistance, R_(e), of the battery per Equation 7 (240). Themethod also includes the step of calculating the integrated in-cellionic resistance, R_(i(ti)), of the battery at the temperature t_(i) perEquation 8 (245). The method also includes the step of calculating theintegrated in-cell ionic resistance, R_(i(tj)), of the battery at thetemperature t_(i) per Equation 8 (250).

Referring to FIG. 3, a battery 310 is shown including a label 320 thathas a voltage indicator, or tester, 330 incorporated within it. Thelabel 320 may be a laminated multi-layer film with a transparent ortranslucent layer bearing the label graphics and text. The label 320 maybe made from polyvinyl chloride (PVC), polyethylene terephthalate (PET),and other similar polymer materials. Known types of voltage testers thatare placed on batteries may include thermochromic and electrochromicindicators. In a thermochromic battery tester the indicator may beplaced between the anode and cathode electrodes of the battery. Theconsumer activates the indicator by manually depressing a switch. Oncethe switch is depressed, the consumer has connected an anode of thebattery to a cathode of the battery through the thermochromic tester.The thermochromic tester may include a silver conductor that has avariable width so that the resistance of the conductor also varies alongits length. The current generates heat that changes the color of athermochromic ink display that is over the silver conductor as thecurrent travels through the silver conductor. The thermochromic inkdisplay may be arranged as a gauge to indicate the relative capacity ofthe battery. The higher the current the more heat is generated and themore the gauge will change to indicate that the battery is good.

Experimental Testing Electrolyte Resistance Measurements

Resistance measurements of the electrolyte are conducted in aresistivity cell that is coupled to a potentiostat and frequencyresponse analyzer at various temperatures. The resistivity cell is Model3403 available from YSI Incorporated that has a cell constant, K, ofabout 1.0. The cell constant of the resistivity cell may be determined,for example, in accord with G. Jones and B. C. Bradshaw, J. Am. Chem.Sec., 55, 1780 (1933). The frequency response analyzer is a Solartron1260 with Solartron 1287 Electrochemical Interface software availablefrom Solartron Group. The electrolyte is an aqueous alkaline electrolytesolution consisting of 31% of potassium hydroxide (KOH) by weight of thesolution and 2% of zinc oxide (ZnO) by weight of the solution that aredissolved in water. The electrolyte is placed in the resistivity cellwithin a temperature-controlled chamber and is allowed to reach themeasurement temperature over the course of approximately one hour. Animpedance sweep from about 100 kHz to about 0.01 Hz is run on theresitivity cell with the electrolyte at temperature. The data resultingfrom the impedance sweep is analyzed with Z-Plot/Z-View ElectrochemicalInterface Software available from Scribner Associates, Inc. Theelectrolyte resistance measurements are completed at a temperature, t₁,of about 5° C.; at a temperature, t₂, of about 15° C.; at a temperature,t₃, of about 30° C.; and at a temperature, t₄, of about 40° C. Theresults of electrolyte resistance measurements, R_(el-te(t1)),R_(el-te(t2)), R_(el-te(t3)), and R_(el-te(t4)), are included in Table 1below.

Ohmic Resistance Measurements

Ohmic resistance measurements are conducted on assembled batteries ofvarying designs at various temperatures. A four-point battery contactfixture is coupled to a potentiostat and a frequency response analyzer.The frequency response analyzer is a Solartron 1260 with Solartron 1287Electrochemical Interface software available from Solartron Group. Abattery is inserted into the four-point battery contact fixture within atemperature-controlled chamber and is allowed to reach the measurementtemperature over the course of approximately one hour. An impedancesweep from about 60 kHz to about 0.1 Hz is run on the fixture includingthe battery at temperature. The data resulting from the impedance sweepis analyzed with Z-Plot/Z-View Electrochemical Interface Softwareavailable from Scribner Associates, Inc. The ohmic resistancemeasurement of the battery is measured by applying an AC potential tothe battery and then measuring the current through the battery. Theimpedance is then represented as a complex number composed of a real andan imaginary part. A Nyquist plot includes the real part, on the X-axis,and the imaginary part, on the Y-axis, of the measured impedance. Theintercept on the X-axis of the impedance is the value of the ohmicresistance of the battery. The ohmic resistance measurements arecompleted at a temperature, t₁, of about 5° C.; at a temperature, t₂, ofabout 15° C.; at a temperature, t₃, of about 30° C.; and at atemperature, t₄, of about 40° C. The background resistance of thefixture is subtracted from the ohmic resistance values that areobtained. The results of ohmic resistance measurements, R_(t1), R_(t2),R_(t3), and R_(t4), are included in Table 1 below.

Testing of Assembled AA Alkaline Primary Batteries

A battery, referred to as Battery A in Table 1, is assembled to evaluatethe effects of the present invention. The anode includes an anode slurrycontaining 4.65 grams of zinc; 1.35 cubic centimeters of a potassiumhydroxide alkaline electrolyte with about 31% KOH by weight and 2% byZnO dissolved in water; 0.027 grams of polyacrylic acid gellant; and0.02 grams of corrosion inhibitor. The cathode includes a blend of EMD,graphite, and potassium hydroxide aqueous electrolyte solution. Thecathode includes a loading of 10.74 grams of EMD, and a loading of 0.4grams Timcal BNB-90 graphite. Battery A also has a cathode-to-anodeinterfacial area. The cathode-to-anode interfacial surface area ofBattery A is 11.253 cm². A separator, having an outer layer and innerlayer, is interposed between the anode and cathode. The outer layer ofthe separator includes a cellophane laminated to a nonwoven materialwith a basis weight of about 57 g/m² and a thickness of about 90 microns(dry). The inner layer of the separator is a nonwoven material with abasis weight of about 25 g/m² and a thickness of about 110 microns(dry). The anode, cathode, and separator are inserted in a housing thatis cylindrical in shape. The housing is then sealed to finish off thebattery assembly process. Ohmic resistance of Battery A is then measuredas is described above. The results of ohmic resistance measurements,R₁₁, R_(t2), R_(t3), and R_(t4), for Battery A are included in Table 1below.

Another battery, referred to as Battery B in Table 1, is assembled toevaluate the effects of the present invention. The anode includes ananode slurry containing 4.8 grams of zinc; 1.39 cubic centimeters of apotassium hydroxide alkaline electrolyte with about 31% KOH by weightand 2% by ZnO dissolved in water; 0.027 grams of polyacrylic acidgellant; and 0.02 grams of corrosion inhibitor. The cathode includes ablend of EMD, graphite, and potassium hydroxide aqueous electrolytesolution. The cathode includes a loading of 10.92 grams of EMD, and aloading of 0.4 grams Timcal BNB-90 graphite. Battery B also has acathode-to-anode interfacial area. The cathode-to-anode interfacialsurface area of Battery B is 11.352 cm². A separator, having an outerlayer and inner layer, is interposed between the anode and cathode. Theouter layer and the inner layer of the separator both include a nonwovenmaterial separator with a basis weight of about 23 g/m² and thickness ofabout 75 microns (dry) The anode, cathode, and separator are inserted ina housing that is cylindrical in shape. The housing is then sealed tofinish off the battery assembly process. Ohmic resistance of Battery Bis then measured as is described above. The results of ohmic resistancemeasurements, R_(t1), R_(t2), R_(t3), and R_(t4), for Battery B areincluded in Table 1 below.

The ratios of the resistances of the electrolyte for all selectedtemperature combinations are calculated per Equation 6 for Battery A andBattery B. The integrated in-cell electronic resistance, R_(e), iscalculated per Equation 7 for Battery A and Battery B for all selectedtemperature combinations. The average of each integrated in-cellelectronic resistance, R_(e), is included in Table 1 below. Theintegrated in-cell ionic resistance, R_(i(t1)), R_(i(t2)), R_(i(t3)),and R_(i(t4)), are calculated per Equation 8 for Battery A and BatteryB. The calculated integrated in-cell ionic resistances are included inTable 1 below.

Area-Specific Resistance Measurements

Area-Specific Resistance measurements are conducted in a resistivitycell at room temperature, e.g., about 21° C. The resistivity cellconsists of two stainless steel electrodes encased in Teflon®. The lowerelectrode is constructed such that a small reservoir of electrolyte maybe maintained in the cell. The top electrode assembly is removable andis aligned to the bottom assembly via two metal pins. The top electrodeassembly is spring loaded so that that force may be applied(approximately 4 to 5 lbs.) to the top of a material sample beinganalyzed. The lower electrode assembly is screwed to a fixture base andelectrical leads are attached to each electrode. The leads are thenattached to the leads of an impedance analyzer, such as a SolartronImpedance Analyzer, that is used to complete impedance sweeps todetermine resistances of the cell or sample materials.

The background resistance of the resistivity cell is determined byrunning an impedance sweep on the fixture filled with electrolyte whenits electrodes are shorted. The sweep starts at 100,000 kHz and finishesat 100 Hz using a 10 mV amplitude, using the software program ZPlot byScribner Instruments to control the instrumentation. The resistance ofthe fixture (R_(CELL)) may have typical values between about 10 and 150mΩ depending upon the condition of the stainless steel electrodes.Several sweeps may be completed to ensure the value obtained isrelatively constant.

The resistance of the separator and electrolyte combination isdetermined by running an impedance sweep on a separator sample. Thefixture includes a center disk upon which the separator sample may beplaced. Electrolyte is placed within the cavity of the resistivity cellto a level that ensures the separator sample is well-wetted on bothsides for 1 minute. The same impedance sweep as described above is run.Again, several sweeps may be completed to ensure the value obtained isrelatively consistent. The data obtained from the sweeps is plotted on aNyquist plot. The ohmic resistance (R_(REAL)) of the separator andelectrolyte combination is determined at the Z″=0 point on the Nyquistplot. However, this value includes the resistance of the resistivitycell. By subtracting the resistance value of the resistivity cell(R_(CELL)) from the resistance determined for the separator andelectrolyte combination sample that includes resistivity cell impedance(R_(REAL)), one can calculate the adjusted resistance value for theseparator and electrolyte combination [R_(REAL)(ADJ)].

The area-specific resistance (ASR) of the separator/electrolytecombination is determined by multiplying the geometrical surface area ofthe resistivity cell's working electrode by the adjustedseparator-electrolyte combination's resistance value. The workingelectrode surface area of resistivity cell used in these experiments is3.83 cm². The units of ASR are mOhm·cm².

The area-specific resistance for the separator and electrolytecombinations of Battery A and Battery B that are described above aremeasured. The impedance of the resistivity cell, at room temperature, isfirst determined with each specific electrolyte as described above. Theimpedance of the separator/electrolyte combination, at room temperature,is then determined with each specific electrolyte. The adjustedseparator/electrolyte combination resistance is then determined and usedin the calculation of the ASR. The ASR for Battery A and Battery B isincluded within Table 1.

Results Discussion

Table 1 includes the data resulting from all analyses that are describedabove.

TABLE 1 Area-specific resistance (ASR) for separator/electrolytecombinations. RESISTANCE BATTERY A BATTERY B R_(el-te(t1)) 3.153 3.006(Ω · cm) R_(el-te(t2)) 2.543 2.428 (Ω · cm) R_(el-te(t3)) 1.948 1.837 (Ω· cm) R_(el-te(t4)) 1.685 1.594 (Ω · cm) R_(t1) 0.056 0.067 (Ω) R_(t2)0.046 0.574 (Ω) R_(t3) 0.035 0.486 (Ω) R_(t4) 0.029 0.446 (Ω) R_(e)0.017 0.019 (Ω) R_(i(t1)) 0.056 0.047 (Ω) R_(i(t2)) 0.046 0.038 (Ω)R_(i(t3)) 0.035 0.029 (Ω) R_(i(t4)) 0.029 0.025 (Ω) ASR 428 326 (mOhm ·cm²) Cathode-to-Anode Interfacial 11.253 11.352 Area (cm²) R_(is) 0.0380.029 (Ω)

The integrated in-cell ionic resistance and the integrated in-cellelectronic resistance of both Battery A and Battery B may beextrapolated for any temperature within the range of 0° C. to 40° C.from the data above. For example, the integrated in-cell ionicresistance and the integrated in-cell electronic of Battery A at 22° C.are 0.041Ω and 0.017Ω respectively. In addition, the integrated in-cellionic resistance and the integrated in-cell electronic of Battery B at22° C. are 0.034Ω and 0.019Ω respectively. The integrated in-cell ionicresistance at 22° C. is greater than the resistance of the electrolytewithin the pores of the separator, R_(is), for both Battery A andBattery B. This may indicate an inefficient dispensing of the anodeslurry within the anode volume of both Battery A and Battery B that maycreate voids within the interface.

The wet thickness of the outer layer of separator for Battery A is about200 μm. The wet thickness of the inner separator for Battery A is 160μm. The effective thickness of the separator, T_(cell), in Battery A at22° C. is 388 μm [(0.041Ω/0.038Ω)·(0.200 μm+0.160 μm)]. The wetthickness of the outer layer of separator for Battery B is about 120 μm.The wet thickness of the inner separator for Battery B is 120 μm. Theeffective thickness of the separator, T_(cell), in Battery A at 22° C.is 281 μm [(0.034 Ω/0.029Ω)·(0.120 μm+0.120 μm)]. The effectivethickness of the separator for Battery A and Battery B is greater thanthe wet thickness of the separator for Battery A and Battery B. This mayalso indicate an inefficient dispensing of the anode slurry within theanode volume of both Battery A and Battery B that may create voidswithin the interface.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application and any patent application or patent to which thisapplication claims priority or benefit thereof, is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document is not an admission thatit is prior art with respect to any invention disclosed or claimedherein or that it alone, or in any combination with any other referenceor references, teaches, suggests or discloses any such invention.Further, to the extent that any meaning or definition of a term in thisdocument conflicts with any meaning or definition of the same term in adocument incorporated by reference, the meaning or definition assignedto that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A primary AA alkaline battery comprising: ananode, the anode comprising an electrochemically active anode material;a cathode, the cathode comprising an electrochemically active cathodematerial; an electrolyte, the electrolyte comprising a hydroxide; and aseparator therebetween the anode and the cathode; and an integratedin-cell ionic resistance (R_(i)) at 22° C. of less than about 39 mΩ;wherein the concentration of the hydroxide within the electrolyte isbetween about 25 weight percent (wt. %) and about 40 wt. %, based on theweight of the electrolyte in the battery, and the separator has aporosity of greater than 70%.
 2. The primary AA alkaline battery ofclaim 1, wherein the hydroxide concentration is between about 25 wt. %and about 32 wt. %.
 3. The primary AA alkaline battery of claim 1,wherein the hydroxide is selected from the group consisting of sodiumhydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, andmixtures thereof.
 4. The primary AA alkaline battery of claim 1, whereinthe electrolyte further comprises zinc oxide.
 5. The primary AA alkalinebattery of claim 4, wherein the concentration of zinc oxide in theelectrolyte is less than 3 wt. %.
 6. The primary AA alkaline battery ofclaim 1, wherein the electrochemically active anode material compriseszinc, the zinc having an anode loading from about 3.3 grams of zinc toabout 5.5 grams of zinc.
 7. The primary AA alkaline battery of claim 1,wherein the anode loading is from about 4.0 grams of zinc to about 5.5grams of zinc.
 8. The primary AA alkaline battery of claim 1, whereinthe anode loading is from about 4.3 grams of zinc to about 5.5 grams ofzinc.
 9. The primary AA alkaline battery of claim 1, wherein the anodeloading is from about 4.6 grams of zinc to about 5.5 grams of zinc. 10.The primary AA alkaline battery of claim 1, the integrated in-cellelectronic resistance (R_(e)) at 22° C. being less than about 22 mΩ. 11.The primary AA alkaline battery of claim 1, the primary AA alkalinebattery further comprising an ohmic resistance (R_(t)) at 22° C. of lessthan about 57 mΩ.
 12. The primary AA alkaline battery of claim 1,wherein the electrochemically active cathode material compriseselectrolytic manganese dioxide.
 13. The primary AA alkaline battery ofclaim 12, wherein the electrochemically active cathode material furthercomprises an electrochemically active material selected from the groupconsisting of manganese oxide, manganese dioxide, electrolytic manganesedioxide (EMD), chemical manganese dioxide (CMD), high power electrolyticmanganese dioxide (HP EMD), lambda manganese dioxide, gamma manganesedioxide, beta manganese dioxide, and mixtures thereof.
 14. The primaryAA alkaline battery of claim 12, wherein the electrochemically activecathode material further comprises an electrochemically active materialselected from the group consisting of silver oxide, nickel oxide, nickeloxyhydroxide, copper oxide, copper salts, bismuth oxide, high-valencenickel compound, high-valence iron compound, and mixtures thereof. 16.The primary AA alkaline battery of claim 12, wherein theelectrochemically active cathode material further comprises anelectrochemically active material selected from the group consisting ofnickel hydroxide, nickel oxyhydroxide, cobalt oxyhydroxide-coated nickeloxyhydroxide, delithiated layered lithium nickel oxide, partiallydelithiated layered nickel oxide, and mixtures thereof.
 17. The primaryAA alkaline battery of claim 12, the electrolytic manganese dioxidehaving a BET surface area from about 15 m²/g to about 35 m²/g.
 18. Theprimary AA alkaline battery of claim 1, the cathode comprising a carbonadditive, the carbon additive comprising between about 2.0 wt. % toabout 10 wt. % of the cathode.
 19. The primary AA alkaline battery ofclaim 1, the separator comprising a density between about 1.30 g/cm³ andabout 1.40 g/cm³.
 20. The primary AA alkaline battery of claim 1, thezinc having a particle size between about 10 μm and about 300 μm. 21.The primary AA alkaline battery of claim 13, the zinc having a BETsurface area from about 0.0410 m²/g to about 0.0600 m²/g.